Electrolytic cell anodes

ABSTRACT

An improved anode for use in electrolytic cells for the production of titanium and zirconium, said anode having a plurality of angular passages extending from one face to the diametrically opposite face.

United States Patent Inventors John C. Priscu;

Eldon R. Poulsen, both of Las Vegas, Nev. 793,680 Jan. 24, 1969 Oct. 26, 1971 Titanium Metals Corporation of America v West Caldwell, NJ.

Appl. No. Filed Patented Assignee ELECTROLYTIC CELL ANODES 5 Claims, 2 Drawing Figs.

204/247, 204/64 T, 204/284 1m. (11.; C22d 3/02, C22d 3/00 Field of Search.........................................204l243247, 68, 4, 284

[ 56] References Cited UNITED STATES PATENTS Re.26,86l 4/1970 Pris-cm... 204/246 1,475,739 11/1923 Brace 204/243 2,111,264 3/1938 Gilbert 204/68 2,921,894 1/1960 O'Callaghan. 204/243 3,079,324 2/1963 Allen et al. 204/247 X 3,374,163 3/1968 Meier et al 204/246 Primary Examiner-John H. Mack Assistant Examiner D. R. Valentine Attorney-Webb, Burden, Robinson 8L Webb ABSTRACT: An improved anode for use in electrolytic cells for the production of titanium and zirconium, said anode having a plurality of angular passages extending from one face to the diametrically opposite face.

'PATENTEDUCT 26 I971 3.616.441

SHEET 1 OF 2 4. m. 0 nm 0 1" O in,

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INVENTORS. John C. Priscu Eldon R. Poulsen THEIR ATTORNEYS ELECTROLYTIC CELL ANODES This invention relates to electrolytic cells for use in the production of titanium and zirconium metal from the tetrachloride of the metal and more. particularly to a specific anode structure for use in these cells.

In electrolytic cells such as that described in US. Pat. No. 3,282,822, fine titanium crystals drain from the cathode assembly into the cell electrolyte when the assembly is withdrawn at the end of each operating cycle, and a portion of these fines falls into the sludge sump at the bottom of the cell; and another portion becomes entrapped between the rear faces of the anode rods and the cell walls. Most of the fines are chlorinated and recovered as TiCl. from the off gas at the beginning of the next cell operating cycle. However, the fines in the sludge sump and entrapped between the anode rods and the cell walls are not affected since no chlorine is generated in these portions of the cell, and, therefore, a gradual buildup occurs. As the accumulation of titanium fines continues, the electrolyte in the sump and between the cell walls and the rear faces of the anode rods becomes increasingly more conductive than the rest of the electrolyte. Eventually the buildup of fines behind the anodes communicates with the fines in the sludge sump, which in turn communicates with the cathode assembly, and the cell is partially short circuited. The partialshort circuiting of the cell decreases cell efficiency and results in the deposit of titanium on the cathode assembly having a very small crystal size. This small crystal size is deleterious as it decreases the amount of titanium obtainable during leaching of the sponge formed in the cell.

Our invention eliminates partial shortcircuitingdue to the buildup of fines in the sump and between the anode rods and the cell wall as chlorine gas is generated on the anode adjacent the brick bottom, and chlorine is permitted toflowbehind the anode rods. This chlorine gas reacts with the titanium fines in the sump and in the space between the anodes and the cell walls and creates titanium tetrachloride which then passes out of the cell in the offgas.

In the accompanying drawings, we have shown a preferred embodiment of our invention in which:

FIG. I is a vertical section through an electrolytic cell, and

FIG. 2 is a section on line ll--ll ofFlG. 1.

Referring to the drawings, the electrolytic cell includes a metal container 1 having refractory sidewalls 2 and a refractory bottom 3 which will resist the corrosive effects of the fused halide salt electrolyte 4. A sump S is formed in the cell bottom to collect titanium fines. The top of container 1 is closed by a metal cover 5 through which a chlorine vent pipe 6 extends. A channel 7 surrounds a central aperture in cover 5 and contains a liquid sealing metal 8 which may be a lead or tin alloy having a low melting point. This sealing arrangement is described and claimed in U.S. Pat. No. 2,871,178 and forms no part of the present invention. A cathode top plate 9 is provided with a depending fiange 10 which extends downwardly into channel 7 forming a sealed joint with liquid metal 8. Cover 5 is electri' cally connected to the negative pole of a source of direct electric current by a contact member 11, and plate 9 is electrically connected with cover 5 by flanges 10. The electrical connection is facilitated by metal alloy 8 contained in channel 7.

Support bars 12 are attached to the underside of plate 9 at their upper ends, and their lower ends are attached to top 13 of a cathode assembly 14 to suspend the cathode assembly within the cell. The dimensions of the cathode assembly are such that the lower ends of the vertical sidewalls terminate in a plane substantially coincident with a plane through the juncture of the cell bottom 3 and the inner faces of the anode rods. Vertical cathode rods 15 having a round horizontal cross section are attached to the underside of the cathode top and extend downwardly within assembly 14. The elements of the cathode assembly supporting bars 12, plate 9 and container cover 5 are made of electrically conductive material such as steel.

A titanium tetrachloride feedpipe I6 is supported by plate 9 and extends downwardly through the top l3 of cathode asscmbl y 14. Pipe [6 is insulated from plate 9 by a ceramic bushing 17. The feedpipe is preferably made of graphite, and tangentially arranged outlets 18 are located in the lower end of the pipe adjacent to the bottom of cathode assembly 14.

Anode rods 20, preferably made of graphite, extendupwardly into the cell through the bottom of container [and terminate immediately below the upper surface of electrolyte-t.

,The anode rodsare spaced between the outer surface of the sidewalls of the cathode assembly and the inner surfaces of refractory walls 2 of container 1 as shown in FIG. 2 of the drawings. The lower ends of rods 20 are exterior of the chamber and are electrically connected. to a common bus bar 21 which is connected by connector '22 to the positive pole of a source of direct electric current.

As can be seen in FIG. 1 of the drawings, each anode rod is fonned with a pair of passageways angling upwardly from the front face of the rod to the rear face of the. rod. The diameter of the passageways may vary, but we have found that a diameter of approximately I inch is advantageous for an anode rod having a diarneter of 6 inches. The passageways extend upwardly at an angle of about 50 to the horizontal. Two passageways are adequate for anode rods having about 5 feet .oftheir length in the electrolyte and such is shown in FIGJ.

However, it should be understood that the number of passageways will vary with the length of the anode rod located in the electrolyte which willin turn vary with the size of the cell. The determining factor in respect of the number of passageways in the anode rods is the ability ofthe passageways to permit chlorine gas to flow from the front face of eachrod to the rear face of the rod. The lowermost passageway in each anode rod should be located closeto the'refractory cell bottom for reasons explained hereinafter.

In operation of the cellto produce titanium metal, a suitable amount of fused halide salt electrolyte is placed inthe cell. The salt may besodium chloride or a eutecticmixture of sodium and potassium chloride or other alkali or alkali metal chlorides. After the molten electrolyte 'is in the container, cathode assembly I4 is lowered intothecell, and thet'lange ll) of the top plate is immersed in molten sealing metal 8 contained in channel 7 to seal the top of the celI.-Dircct current connections are made from a suitable power supply (not shown) to cover 5 by connector II and to anodes 20 by bus bar 21 and connector 22. Titanium tetrachloride feedpipe I6 is connected atits external end to a source of TiCl, which is fed into the feedpipe and exits through outlets 19 in the lower end of the pipe. Titanium metal is deposited on the members of cathode assembly 14; and when the interior of the cathode assembly is substantially filled with titanium metal, the TiCl. supply is shut off, and the .cathode assembly is removed from the cell. A similar operation may be conducted to produce zirconium metal except that zirconium tetrachloride will be used in place of titanium tetrachloride.

During the electrolysis of the TiCl,, chlorine gas is generated on the portion of the face of each anode rod which is opposite to the cathode assembly. The chlorine is strongly generated at the edges of the passageways on the low side; and due to the angle at which the passageways extend through the anode rods, a certain amount of chlorine is diverted to the rear face of each anode rod. This results in the chlorination of titanium fines located between the rear surfaces of the anode rods and the refractory walls of the cell Additionally, the location of the lower passageway adjacent to the refractory bottom results in chlorine generation in the area of the sump adjacent to the lower end of the anode, and chlorination of a portion of the fines in this area takes place. The reaction of the titanium fines and chlorine produces titanium tetrachloride as the final product, and this passes from the cell through vent pipe 6 along with chlorine in the off gas. The titanium tetrachloride is then separated from the chlorine by a chilled scrubber in accordance with well-known procedures. Thus, titanium fines are removed from adjacent the lower ends of the anodes and from the portion of the electrolyte behind the anodes, and partial short circuiting of the cell is eliminated.

in utilizing our invention, a standard electrolytic cell was operated in accordance with normal procedure except that anode rods having passageways as disclosed heretofore were installed. When the cell was shut down, the electrolyte was drained, and the space between the rear faces of the anode rods and the refractory wall of the cell was then checked for titanium buildup. No buildup of fines was found and no impairment of crystal size was obtained in the deposited titanium during operation of this cell.

Our invention is advantageous in that it increases the efficiency of cell operation since the buildup of fines between the cell walls and the rear faces of the anodes is eliminated, and the desired crystal size is obtained in the titanium metal deposited on the cathode assembly. The invention requires no additional apparatus than that required for normal cell operation and has no effect upon the rate of deposition of metal on the cathode assembly.

While we have shown and described a preferred embodiment of our invention, it should be understood that it may be otherwise embodied within the scope of the appended claims.

We claim:

1. In an electrolytic cell for the production of metal of the group consisting of titanium and zirconium by electrolysis including a container having 'a'iefractory bottom and refractory sidewalls for holding a fused halide salt electrolyte and adapted to exclude ambient atmosphere therefrom, a cathode assembly having perforate sidewalls, a feeclpipe for introducing tetrachloride of the metal into the cathode assembly, a plurality of anode rods immersed in the electrolyte surrounding said cathode assembly and having a face directed towards said cathode assembly and a face directed toward a sidewall of said container, means for venting gas from said container, means for connecting the positive pole of a source of direct current to said anode rods and the negative pole of said current source to said cathode assembly, the improvement comprising a plurality of angular passageways formed in each of said anode rods, each of said passageways directed upwardly from the face of said anode rod facing toward said cathode assembly to the face of said anode rod facing toward a sidewall of said container, whereby chlorine gas generated on the faces of said anodes directed toward said cathode assembly passes upwardly through said passageways to the area between the faces of said anodes directed toward the sidewalls of said container and the sidewalls of said container.

passageways to the horizontal and have a 

2. Apparatus as set forth in claim 1 wherein the lowermost passageway in each rod is adjacent to the bottom of said cell.
 3. Apparatus set forth in claim 1 wherein said passageways extend at an angle of about 50* to the horizontal.
 4. Apparatus set forth in claim 1 wherein said passageways have a diameter of about 1 inch.
 5. Apparatus set forth in claim 1 wherein said passageways extend at an angle of about 50* to the horizontal and have a diameter of about 1 inch. 